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In the last years, a relationship has been established between the quantum Fisher information (QFI) and quantum entanglement. In the case of two-qubit systems, all pure entangled states can be made useful for sub-shot-noise interferometry…

Quantum Physics · Physics 2019-11-11 Stefano Scali , Roberto Franzosi

While all bipartite pure entangled states violate some Bell inequality, the relationship between entanglement and non-locality for mixed quantum states is not well understood. We introduce a simple and efficient algorithmic approach for the…

Quantum Physics · Physics 2009-11-07 Barbara M. Terhal , Andrew C. Doherty , David Schwab

We explore the subtle relationships between partial separability and entanglement of subsystems in multiqubit quantum states and give experimentally accessible conditions that distinguish between various classes and levels of partial…

Quantum Physics · Physics 2008-09-03 Michael Seevinck , Jos Uffink

Kernel mean embedding is a useful tool to represent and compare probability measures. Despite its usefulness, kernel mean embedding considers infinite-dimensional features, which are challenging to handle in the context of differentially…

Machine Learning · Computer Science 2022-06-24 Margarita Vinaroz , Mohammad-Amin Charusaie , Frederik Harder , Kamil Adamczewski , Mijung Park

Variational algorithms have received significant attention in recent years due to their potential to solve practical problems using noisy intermediate-scale quantum (NISQ) devices. A fundamental step of these algorithms is the evaluation of…

Multipartite entanglement detection is crucial for the develop of quantum information science and quantum computation, communication, simulation and metrology tasks. In contrast to experiments, where several handreds of qubits have been…

Quantum Physics · Physics 2024-11-06 Xiao-yu Chen

Experimental progress in qubit manufacturing calls for the development of new theoretical tools to analyze quantum data. We show how an unsupervised machine-learning technique can be used to understand short-range entangled many-qubit…

Quantum Physics · Physics 2023-03-22 Nicolas Sadoune , Giuliano Giudici , Ke Liu , Lode Pollet

Quantum computers are a highly promising tool for efficiently simulating quantum many-body systems. The preparation of their eigenstates is of particular interest and can be addressed, e.g., by quantum phase estimation algorithms. The…

Quantum Physics · Physics 2025-08-28 Xiaoyu Liu , Benjamin F. Schiffer , Jordi Tura

We examine the possible states of subsystems of a system of bits or qubits. In the classical case (bits), this means the possible marginal distributions of a probability distribution on a finite number of binary variables; we give necessary…

Quantum Physics · Physics 2015-06-26 Paul Butterley , Anthony Sudbery , Jason Szulc

The study of non-locality is fundamental to the understanding of quantum mechanics. The past 50 years have seen a number of non-locality proofs, but its fundamental building blocks, and the exact role it plays in quantum protocols, has…

Quantum Physics · Physics 2015-11-06 Stefano Gogioso , William Zeng

We present the generalized state-dependent entropic uncertainty relations in multiple measurements setting, and the optimal lower bound is obtained by considering different measurement sequences. We then apply this uncertainty relation to…

Quantum Physics · Physics 2023-06-05 Li-Hang Ren , Yun-Hao Shi , Jin-Jun Chen , Heng Fan

The barren plateau phenomenon is one of the main obstacles to implementing variational quantum algorithms in the current generation of quantum processors. Here, we introduce a method capable of avoiding the barren plateau phenomenon in the…

Current noise levels in physical realizations of qubits and quantum operations limit the applicability of conventional methods to characterize entanglement. In this adverse scenario, we follow a quantum variational approach to estimate the…

Quantum Physics · Physics 2022-09-16 A. D. Muñoz-Moller , L. Pereira , L. Zambrano , J. Cortés-Vega , A. Delgado

We prove that the threshold detection efficiency for a loophole-free Bell experiment using an $n$-qubit Greenberger-Horne-Zeilinger state and the correlations appearing in the $n$-partite Mermin inequality is $n/(2n-2)$. If the detection…

Quantum Physics · Physics 2009-07-28 Adan Cabello , David Rodriguez , Ignacio Villanueva

Many hybrid quantum-classical algorithms for the application of ground state energy estimation in quantum chemistry involve estimating the expectation value of a molecular Hamiltonian with respect to a quantum state through measurements on…

We consider a Quantum Computer with n quantum-bits (`qubits'), where each qubit is coupled independently to an environment affecting the state in a dephasing or depolarizing way. For mixed states we suggest a quantification for the property…

Quantum Physics · Physics 2008-12-18 Dominik Janzing , Thomas Beth

Recently, there have been several advancements in quantum algorithms for Gibbs sampling. These algorithms simulate the dynamics generated by an artificial Lindbladian, which is meticulously constructed to obey a detailed-balance condition…

Quantum Physics · Physics 2025-12-02 Štěpán Šmíd , Richard Meister , Mario Berta , Roberto Bondesan

We construct an important missing piece in the entanglement theory of pure three-qubit states, which is a polynomial measure of W-entanglement, working in parallel to the three-tangle, which is a polynomial measure of GHZ-entanglement, and…

Quantum Physics · Physics 2025-12-12 Szilárd Szalay

In order to assess whether quantum resources can provide an advantage over classical computation, it is necessary to characterize and benchmark the non-classical properties of quantum algorithms in a practical manner. In this paper, we show…

Constructing local hidden variable (LHV) models for entangled quantum states is challenging, as the model should reproduce quantum predictions for all possible local measurements. Here we present a simple method for building LHV models,…

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